Learning Forum

[Chi-Wei Lee]

Hello guys, 

I'm attempting to calculate the capacitance of two coplanar plates placed on silicon, but I'm unsure whether I should add the region in my configuration. The electric field plot without the added region looks good, whereas adding the region creates an unreasonable electric field. However, in the PowerPoint provided by Ansys, they successfully obtained the capacitance of two parallel plates without considering the surrounding region. I've also confirmed that including the region would alter the resulting value. Additionally, I can't figure out why reducing the size of the region would increase the capacitance I simulated, assuming both regions are large enough.

[Timos]

Could you provide further details about the unreasonable electrical field when adding the region?

To gain more information about the capacitance calculations and the resulting alterations, please visit  Maxwell Help > Maxwell 2D Technical Notes > Electrostatic Field Simulation > Capacitance

[Chi-Wei Lee]

Hello, thank you for your response. The unrealistic field could potentially be a simulation error, and I've included the simulation results below for your review. Figure 1 depicts the design of my device, while figure 2 shows the result obtained with the added region. In contrast, figure 3 presents the result without adding the region.

In reference to the documentation you provided, Maxwell's method involves computing the capacitance by analyzing the electric field and the energy stored within it. As evident in figure 5, the electric field significantly diminishes outside my device, and I've selected a rather spacious region. Therefore, in theory, the region shouldn't have a substantial impact on my results.

However, I've encountered an unexpected discrepancy: the capacitance calculated from figure 2 is 0.164pF, whereas the capacitance derived from figure 3 is 0.774pF. This significant alteration in results is puzzling.

[Chi-Wei Lee]

Hello, thank you for your response. The unrealistic field could potentially be a simulation error, and I've included the simulation results below for your review. Figure 1 depicts the design of my device, while figure 2 shows the result obtained with the added region. In contrast, figure 3 presents the result without adding the additional region.

In reference to the documentation you provided, Maxwell's method involves computing the capacitance by analyzing the electric field and the energy stored within it. As evident in figure 4, the electric field significantly diminishes outside my device, and I've selected a rather spacious region. Therefore, in theory, the region shouldn't have a substantial impact on my results.

However, I've encountered an unexpected discrepancy: the capacitance calculated from figure 2 is 0.164pF, whereas the capacitance derived from figure 3 is 0.774pF. This significant alteration in results is puzzling.

[Timos]

Hello, the region that you introduced is unreasonably huge. Additionally, the Electric Field is not unreasonable, because these plots do not depict precisely the difference between those 2 models. Did you assign any mesh operations? A coarse or poorly refined mesh can lead to inaccurate results.